First of all be strong. You want to leave. You want to breathe. You want your space. Be firm about it. Don’t let anything change that. He cheated on you with the sex chat. You can not trust someone like that. If he truly loved you, he would have never cheated in the first place. He is an insecure man. Thats exactly why he checks your mail and your phone. But he doesn’t let you check his. Why? Because he is probably doing something and he is scared you’d do the same. Why do you want to be his back up plan? He doesn’t love you. He is obsessed with you. You need to breathe. You are successful. You will find a better guy. You are way out of his league.
But let me tell you, you need to be VERY careful. You can’t just pick up the phone and say you want to leave. He seems unstable. You need to first reduce you interaction with him. And stop meeting him completely. Do not meet him at any cost. And slowly cut off from him. You dont want him turning into a psycho. Just do this real slow till he gets over you.
Be careful and be strong!